A common problem when gravel packing is that the gravel forms bridges and leaves gaping areas uncovered as the gravel that is subsequently delivered piles up behind the bridge or blockage. Another problem is the difficulty in delivering screen into long horizontal runs because of the limited weight available to advance the screen and the possibility that it may simply buckle in the wellbore and cease to further advance. Yet another issue is the need to centralize the screen as the gravel is delivered for deposition all around it. Another concern is damage to the screen assembly during run in. Gravel screens have been provided in the past with surrounding shrouds but the delivery to the desired location could still cause damage to the shroud and the underlying screen. Bridge formation is always a concern. Annular bridge formation can be aggravated by zones of low flow rates leading to deposition of undue amounts of gravel in concentrations in undesirable locations leading to a bridge ultimately forming.
In the past, a solid auger on a gravel pack screen has been used to insert the screen into the wellbore after the gravel has been earlier deposited. The auger helps to advance the screen into the borehole location that is already pre-charged with gravel. This method is illustrated in U.S. Pat. No. 5,036,920. Augers have been used on perforating guns to get them out after they are fired, as illustrated in U.S. Pat. Re. 34,451.
Alternate paths for the gravel comprising longitudinally oriented narrow passages disposed parallel to each other have been used to try to deliver gravel beyond a sand bridge. Some examples are U.S. Pat. Nos.: 6,298,916; 5,161,618; 6,059,032; 5,842,516; 4,945,991; 5,161,613; 5,113,935; 5,419,394; 5,417,284; 5,435,391; 5,560,427; 5,848,645; 5,622,224; 5,588,487; 5,890,533; 6,227,303; 6,220,345; 5,476,143; 5,341.880; 5,515,915; 5,082,052; 6,409,219; 5,390,966; and 5,868,200. Also of interest is the Halliburton multiple path screen system called SurePac. Some of these references have shunt tubes that are internal and others feature external tubes. These designs address the specific problem of bridging but ignore some of the other issues such as protection of the screen, advancement of the screen into position and the potential damage to the shunt tubes when mounted externally.
The present invention addresses in a cohesive design several parameters. The hollow flight or flights of augers are structurally rigid to allow rotation to advance the screen. The passages in the flights are also protected by the rigidity of the auger design. The screen is better protected during run in. The auger allows gravel to enter and exit in multiple locations to allow gravel to bypass bridges. The spiral flow pattern in the interior and along the exterior of the auger is more turbulent due to the centrifugal force from going around the screen, making it less likely that gravel will deposit within the auger or prematurely in the annulus. The auger centralizes prior to gravel delivery.
The other advantages are offered by an alternative embodiment that features spirally wound shunt tubes. These tubes are open at discrete locations for escape of gravel. The spiral layout improves gravel distribution upon exit from the tubes.
These and other advantages of the present invention will be more apparent to those skilled in the art from a review of the description of the preferred embodiment and the claims, which appear below.